1. Field of the Invention
The present invention relates to a semiconductor laser in an information recording/reproducing apparatus using an optical disk, and to a countermeasure for heat radiation for a drive circuit of a semiconductor laser.
2. Description of the Related Art
A semiconductor laser (hereafter, simply referred to as an “LD”), which is a light source of an optical disk apparatus, is well known for posing various problems due to temperature rise, such as shortening of lifetime, degradation of signal quality involved in an increase of quantum noise, and lowering of a slope efficiency showing a relation between a drive current and an emission efficiency.
Further, an LD and a driver for driving an LD (hereafter, simply referred to as an “LDD”) are connected to each other on an electrical circuit board, and are generally subjected to an influence of an electrical noise as the distance therebetween becomes larger, whereby the degradation of the signal quality occurs. As a result, in order to improve the signal quality, it is necessary to dispose the LD and the LDD as close to each other as possible, on an optical pickup to be described later.
However, on the optical pickup, an LD and an LDD are main heat generating sources. Therefore, when the LD and the LDD are disposed close to each other, heat is transferred therebetween to thereby accelerate the temperature rise of each of the components.
Furthermore, in recent years, it has been necessary to reduce the size and the thickness of the optical disk apparatus. This requirement is especially remarkable in the field of mobile applications, such as disk camcorders that have been commercialized recently, in which components, such as an optical disk apparatus and an electrical board, are accommodated in an outer package of a product at a high density. Accordingly, the temperature rise of the optical disk apparatus is prompted, whereby a temperature rise of the LD is generated.
Furthermore, the components themselves must be reduced in the size and thickness thereof, which causes degradation of the heat radiation performance, involved in the lowering in the heat capacity of the components.
As described above, temperature environments surrounding an LD have become worse and worse. Therefore, it is necessary to improve the conflicting functions described above of “taking a countermeasure against electrical noise and reducing a thermal influence between heat generating sources” and of “reducing the sizes of components themselves and improving the heat radiation performance” at the same time.
As the technology for accomplishing the tasks described above, two conventional technologies are exemplified as follows.